Implantable occlusion system

ABSTRACT

An occlusion system implantable in a human or animal body, including a fluidic circuit which includes an inflatable occlusive sleeve, a reservoir with variable volume filled with a fluid. The reservoir includes a fixed portion and a movable portion, an actuator mechanically coupled with the movable portion of the reservoir to linearly displace the movable portion relative to the fixed portion for adjusting the volume of the reservoir. The actuator and the reservoir are laid out in a sealed casing containing a gas. A sensor mechanically bound to the actuator and/or to the movable portion, measures a traction and/or compressive force of the movable portion of the reservoir. Also included is a device for measuring the fluid pressure in the fluidic circuit.

FIELD OF THE INVENTION

The present invention relates to an implantable occlusion system in ahuman or animal body.

BACKGROUND OF THE INVENTION

It is known how to occlude an anatomic conduit by means of an occlusionsystem implantable into the body of a patient.

The occlusion of the anatomic conduit is ensured by an inflatable sleevefilled with fluid which exerts a more or less strong pressure on theportion to be occluded depending on the volume of the fluid in theinflatable sleeve.

For example, various urinary artificial sphincters are based on thisprinciple for exerting pressure on the urethra. Among known products,mention may be made of the implant referenced as AMS800 marketed byAmerican Medical Systems or else the implant referenced as ZSI375marketed by Zephyr. The same principle is found in other types ofapplications such as gastric rings which include an inflatable sleeveplaced around the stomach.

The swellable sleeve filled with fluid may be made in different forms,for example totally or partly surrounding the conduit to be occluded andmay be formed with different biocompatible materials, such asimplantable silicone, implantable polyurethane, etc.

The injection and the suction of fluid in the inflatable sleeve requiredfor the occlusion of the anatomic portion may be either achievedmanually and passively such as for artificial urinary sphincters AMS800and ZSI375, or automatically and actively (from an electric power sourcefor example) for more developed implants.

In order to allow regulation of the pressure exerted on the conduit tobe occluded, the inflatable sleeve is in fluidic connection with areservoir of fluid coupled with a configured actuator for injectingfluid from the reservoir to the sleeve (in order to increase thepressure exerted on the anatomic conduit) or from the sleeve to thereservoir (for reducing the pressure exerted on the anatomic conduit).The whole of the inflatable sleeve, of the reservoir and of the fluidicconnection between them forms a fluidic circuit.

In such an occlusion system, it may be necessary to measure the pressurein the inflatable sleeve or in another point of the fluidic circuit, forexample in order to check pressure when the actuator is disabled, orfurther for controlling the pressure generated by said actuator.

Document EP 1 584 303 thus discloses the use of a pressure sensorimplanted on the occlusive sleeve. However such a solution cannot beachieved industrially since it poses problems of integration, bulkiness,seal and biocompatibility of the sensor.

For this purpose, there exist different types of pressure sensors.

Among the sensors which may be contemplated in an implantable system,pressure sensors based on a flexible membrane in contact with the fluidmay be used. These sensors nevertheless have to be biocompatible, stableover time, and it is necessary to ensure a perfect seal of the sensor inorder to avoid infiltration of fluid or of humidity into the sensor orthe associated electronics.

A solution to this problem may be the use of a pressure sensorcomprising a flexible metal membrane ensuring the seal of the system.However, such a sensor has several drawbacks. On the one hand, as themetal membrane of the sensor is thin, the manufacturing methods may bedelicate. Indeed, the mechanical stresses due to thermal effects of theweld on the membrane may have an effect on the stiffness of the membranewhich may induce significant disparities in the mechanical properties ofthe membrane. Moreover, this type of sensor is generally sealed andfilled with a non-compressible fluid in contact with a pressure sensorstrictly speaking. The method for assembling the different portions ofthe system (consisting of several tens of elements) is thereforedelicate and costly. Finally, when the system is implanted, the fibrosissurrounding the different elements of the implant may induce a change instiffness of the membrane and therefore a drift in the measurements overtime.

Another problem to be solved is to be able to apply a defined andspecific pressure on the anatomic conduit by consuming a minimum ofenergy.

A simple solution would be to use a system based on the measuredocclusion pressure. Among the means for measuring the occlusionpressure, mention may be made of systems which directly measure thepressure in the fluidic circuit via a suitable sensor, or else whichmeasure the pressure indirectly for example from the current consumed bythe actuator as described in document U.S. Pat. No. 8,585,580.

However, it has been demonstrated by tests in vivo [1] that the pressurein the fluidic circuit strongly and permanently varies during theocclusion. In the case of a system based on a pressure regulation, thishas the effect of quasi-permanently urging the actuator for stabilizingthe pressure at a given set value, with the consequence of inducingexcessive electric consumption of the system.

Other principles have been proposed, for example document U.S. Pat. No.8,585,580 proposes a system which transfers a fluid to the inflatablesleeve until the measured pressure exceeds a defined threshold. Thissolution has the drawback of not being very accurate on the appliedocclusion pressure. Indeed, during the occlusion phase, the pressure maystrongly increase and then decrease due to the relaxation of the tissuesand of the occlusion device. The fluid provided to the occlusion devicein contact with the anatomic conduit to be occluded is thereforegenerally not sufficient for generating the desired pressure.

Moreover, the bulkiness of such a sensor also poses a problem, insofarthat the implantable system has to be of dimensions as reduced aspossible and that said system further comprises a fluid transfer device,the volume of which has to be consequent and a battery which alsorepresents a large portion of the volume of the implantable system. Theintegration of such a sensor into this system may be difficult due tothe bulkiness of said sensor. Further, as this type of sensor has to beboth in contact with the outside, and for the pressure measurement, andwith the inside for communicating with the electronic module, it isnecessary to apply a reliable and hermetic manufacturing process, suchas laser welding, which may be a constraint in a production phase.

SHORT DESCRIPTION OF THE INVENTION

An object of the invention is to design an implantable occlusion systemwhich gives the possibility of getting rid of the drawbacks of theexisting systems. In particular, this system should allow measurement ofthe pressure in the sleeve reliably while being biocompatible, sealedand minimizing the bulkiness of the implantable system and theconsumption of energy required for regulating this pressure. Preferablysaid system should also allow control of the pressure in the sleeve.

For this purpose, an occlusion system is proposed, which is implantablein a human or animal body, comprising:

-   -   a fluidic circuit comprising:        -   an inflatable occlusive sleeve containing a variable volume            of a fluid, intended to surround at least one portion of the            natural conduit to be occluded,        -   a reservoir with variable volume filled with a fluid, said            reservoir comprising a fixed portion and a movable portion,        -   a fluidic connection between the reservoir and the occlusive            sleeve,    -   an actuator mechanically coupled with the movable portion of the        reservoir so as to linearly displace said movable portion        relatively to the fixed portion for adjusting the volume of the        reservoir,

the actuator and the reservoir with variable volume being laid out in asealed casing containing a gas.

According to the invention, said system further comprises:

-   -   a sensor laid out in the casing, mechanically connected to the        actuator and/or to the movable portion of the reservoir, laid        out so as to measure a traction and/or compression force in the        direction of displacement of the movable portion of the        reservoir, said measured force resulting at least from:        -   the force noted as F_(occl) exerted on the movable portion            of the reservoir with a variable volume related to the            pressure in the fluidic circuit, and        -   the force noted as F_(casing) exerted on the movable portion            of the reservoir with variable volume related to the            pressure in the casing,    -   a device for measuring the fluid pressure in the fluidic circuit        comprising a processing unit configured for determining said        fluid pressure from a calculation taking into account at least        the force measured by said sensor, the effective pressure        surface of the movable portion of the reservoir, and the force        F_(casing) exerted on the movable portion of the reservoir with        a variable volume related to the gas pressure in the casing.

This system has the following advantages. On the one hand, the fact thatthe sensor is laid out in the casing, allows measurement of the pressurewithout any remote element (outside the casing) and therefore avoidsapplication of complex connections leaving the casing and the seal ofwhich has to be ensured. Further, biocompatibility is ensured by thecasing and therefore does not generate any specific constraint in termsof the design of the sensor. Finally, as the sensor is integrated to thepressurization system of the sleeve, the required bulkiness isminimized.

According to a preferred embodiment, the system further comprises adevice for controlling the fluid pressure in the fluidic circuit by thevolume of the reservoir, comprising:

-   -   a memory in which is recorded a relationship between the        pressure in the fluidic circuit and the volume of said        reservoir,    -   a processing unit configured for:        -   receiving a fluid pressure set value in the fluidic circuit,        -   from the relationship recorded in the memory between the            pressure in the reservoir and the volume of the reservoir,            determining the volume of the reservoir with which it is            possible to attain the pressure set value,        -   if necessary, controlling the actuator for displacing the            movable portion of the reservoir into a position defining            said determined volume,    -   a calibration unit configured for:        -   (a) when the patient is in a determined situation,            controlling the actuator for displacing the movable portion            of the reservoir into a plurality of determined positions,            each position defining a determined volume of the reservoir,        -   (b) for each of said positions:            -   measuring the fluid pressure in the fluidic circuit by                said device for measuring the fluid pressure in the                fluidic circuit,            -   updating the memory by recording said fluid pressure                measured in the fluidic circuit for the respective                volume of the reservoir.

According to an embodiment, the sensor is able to measure tractionforces and the compressive forces in the direction of displacement ofthe movable portion of the reservoir.

According to another embodiment, the sensor is able to exclusivelymeasure compressive forces in the direction of displacement of themovable portion of the reservoir; in this case, the system furthercomprises a pre-stress device laid out so as to exert a determinedcompressive pre-stress on said sensor.

In this case, the processing unit is configured for taking into accountsaid pre-stress for determining the fluid pressure in the fluidiccircuit.

The pre-stress device advantageously comprises at least one compressivespring, a traction spring and/or an elastomeric pad.

According to an embodiment, the movable portion of the reservoir with avariable volume comprises a driving system coupled with a movable walland deformable bellows extending and being compressed according to theposition of said movable wall.

In this case, the processing unit is advantageously configured so as totake into account the stiffness of said bellows for determining thefluid pressure in the fluidic circuit.

In an advantageous embodiment, the drive system comprises a screwsecured to the movable wall and a nut coupled with the screw androtatably movable on a dual-effect bead abutment around the axis of thescrew under the effect of a driving action by the actuator, the nutbeing coupled with the screw so that rotation of the nut only drives thescrew into translation in the displacement direction of the movableportion; moreover, the sensor is laid out in said bead abutment so as tomeasure at least one traction force and one compression force in thedisplacement direction of the movable portion of the reservoir.

According to another embodiment, the movable portion of the reservoirwith a variable volume comprises a driving system coupled with a rollingmembrane.

According to another embodiment, the reservoir with a, variable volumecomprises a cylinder forming the fixed portion of the reservoir and apiston sliding in said cylinder, forming the movable portion of thereservoir.

Advantageously, the actuator is selected from piezoelectric actuators,electromagnetic actuators, electro-active polymers and shape memoryalloys.

According to an embodiment of the invention, the system furthercomprises a gas pressure sensor laid out in the casing for measuring thegas pressure in the casing, the processing unit being configured fortaking into account said gas pressure measured in the determination ofthe force F_(casing).

Advantageously, a wall of the reservoir with a variable volume is formedby a wall of the casing, said wall comprising a perforable punctureport.

Advantageously, the system further comprises a device for reducingstresses in the fluidic circuit when said stresses exceed a determinedthreshold.

According to a preferred embodiment, the system further comprises anaccelerometer, the processing unit being configured for determining frommeasurement data of the accelerometer, whether the patient is in adetermined situation.

More advantageously, the device for measuring the pressure is configuredfor measuring the fluid pressure upon adjusting the volume of thereservoir and for checking the match between said measured value and anexpected value.

According to a preferred embodiment of the invention, the system is anartificial urinary sphincter.

According to an embodiment, the treatment unit is configured forcalculating a relative fluid pressure in the fluidic circuit, saidrelative pressure being equal to the difference between the fluidpressure determined in the fluidic circuit and the atmospheric pressureexerted on the patient.

According to an embodiment, the system further comprises a deviceintended to be placed outside the body of the patient and comprising abarometric sensor suitable for measuring the atmospheric pressureexerted on the patient, said device being able to communicate saidpressure measurement to the treatment unit for calculating said relativefluid pressure in the fluidic circuit.

Alternatively, the treatment unit is configured for determining theatmospheric pressure exerted on the patient from the pressure in thefluid circuit and from a known relative pressure of the fluid in thefluidic circuit in a given actuation configuration of the sleeve.

SHORT DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will become apparent fromthe detailed description which follows, with reference to the appendeddrawings wherein:

FIG. 1 is an overall view of the implantable occlusion system,

FIG. 2 is a sectional view of the inside of the casing of an implantableocclusion system according to a first embodiment of the invention,

FIG. 3 is a sectional view of the casing of an implantable occlusionsystem according to a second embodiment of the invention,

FIG. 4 is a sectional view of the casing of an implantable occlusionsystem according to a third embodiment of the invention,

FIG. 5 is a sectional view of the inside of the casing of an implantableocclusion system according to a fourth embodiment of the invention,

FIG. 6 is a diagram showing the different forces which may be measuredby the compressive or traction force sensor, in the presence of apre-stress,

FIG. 7 is a diagram showing the various forces which may be measured bythe compressive and traction force sensor in the absence of anypre-stress,

FIG. 8 is a graph showing the variation of the pressure in the fluidiccircuit depending on the volume injected into the occlusive sleeve,

FIG. 9 is a graph showing the variation of the pressure in the fluidiccircuit versus time for different volumes of fluid injected into theocclusive sleeve during the calibration procedure.

FIG. 10 is a sectional view of the casing of an implantable occlusivesystem according to a fifth embodiment of the invention.

FIG. 11 is a sectional view of the force sensor and of the actuator ofthe system of FIG. 10, with an illustration of the measured forces.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

General Presentation of the Implantable Occlusion System

With reference to FIG. 1, the occlusion system comprises an inflatableocclusive sleeve 3 containing a variable volume of a fluid, intended tosurround at least one portion of a natural conduit (not shown) to beoccluded, and a reservoir 5 with a variable volume (illustrated in FIGS.2 to 5) filled with a fluid.

The occlusive sleeve may be made of a biocompatible elastomer (cf. forexample documents U.S. Pat. No. 4,222,377, CA 1,248,303 or U.S. Pat. No.4,408,597).

Said reservoir comprises a fixed portion and a movable portion, thedisplacement of the movable portion varying the volume of the reservoir.

For this purpose, the occlusion system comprises an actuatormechanically coupled with the movable portion of the reservoir so as tolinearly displace said movable portion relatively to the fixed portionin order to adjust the volume of the reservoir. The actuator may notablycomprise an electromagnetic motor and a reducer. The actuator iscontrolled by a device for controlling the pressure of the sleeve whichwill be described in detail later on.

For each volume of the reservoir, the movable portion has a knowneffective pressure surface area, which may be constant or variableaccording to the embodiments.

The occlusion system further comprises a fluidic connection 2 (typicallytubing) between the reservoir 5 and the occlusive sleeve 3.

Thus, a variation in volume of the reservoir 5 causes addition orwithdrawal of fluid in the sleeve 3, thereby increasing or decreasingthe compression exerted on the conduit surrounded by the sleeve.

The assembly formed with the reservoir of variable volume, of theocclusive sleeve and of the fluidic connection is called a fluidiccircuit in the following of the description.

In addition to the device for controlling the pressure of the occlusivesleeve, the implantable system includes one or several electronicmodules giving the possibility of producing all the required functions.It further includes a rechargeable power source or not, allowing thesystem to be powered. In a particular configuration, the power source isoutside the human body and transmits the energy in a wireless way to theimplantable system.

The reservoir with variable volume, the actuator as well as saidelectronic module(s) and, if necessary, the power source, are laid outin a casing 1 intended to be implanted into the body of the patient. Thecasing 1 contains a gas, for example air, said casing has to be sealedso as to avoid any transfer of fluid or gas from or to theintracorporeal medium. The casing is in a biocompatible material, andmay for example be made in implantable titanium and sealed by laserwelding. A check of the seal may notably be achieved with helium (forexample, a leak rate of less than 10⁻⁹ mbar·L/s of helium) for ensuringthe total seal of the casing during the period for which the device isimplanted.

According to a particular embodiment, the casing may contain a gaspressure sensor, the function of which will be described below.

Advantageously, the casing 1 comprises, in a wall delimiting thereservoir with a variable volume, a puncture port 4 which may beperforated with a needle and able to sealably close after withdrawingthe needle, allowing injection or withdrawal of the fluid of thereservoir.

The casing also contains a sensor in a mechanical connection with theactuator and/or the movable wall of the reservoir with a variable volumewhich may measure a compressive and/or traction force in the directionof displacement of the movable portion of the reservoir.

Among the sensors suitable for this use, mention may for example be madeof:

-   -   a sensor based on one or several strain gauges (such gauges        allow measurement of traction and compressive forces);    -   one or several sensors of the FSR™ type (acronym “Force Sensing        Resistor”) marketed by Interlink Electronics, measuring        compressive forces); and/or    -   one or several pressure sensors coupled with a mechanism        allowing measurement of a force. For example, mention may be        made of a hydraulic pressure sensor combined with a pocket full        of fluid and laid out so as to measure a pressure on a        predetermined surface, thereby allowing inference of the force        applied to the measurement surface.

The system may further comprise a device allowing measurement of theatmospheric pressure in the surroundings of the patient. A barometricsensor capable of measuring the current atmospheric pressure exerted onthe body of the patient, may for example be laid out in an externaldevice borne by the patient. This measurement may be transmitted by awireless link to the control device laid out in the implantable casing.

Reservoir with a Variable Volume

According to a preferred embodiment, the reservoir with a variablevolume comprises bellows assembled in the casing, the bellows and thecasing for example being made in implantable titanium. The reservoirwith variable volume then consists of the bellows (acting as a movableportion), of a wall of the casing and of a hood acting with said wall ofthe casing, as a fixed portion. The reservoir further comprises anorifice allowing transfer of the fluid from and to the outside of thereservoir.

The use of metal bellows for producing the function of a reservoir withvariable volume is known to the person skilled in the art (cf. documentU.S. Pat. No. 4,581,018 for example). Such bellows are for examplemarketed by Servometer and Witzenmann.

The bellows have the advantage of ensuring total seal of the implantwhile allowing movement of the movable wall. Its effective pressuresurface area may be considered as constant over the whole range oftravel of the bellows.

Nevertheless, it should be taken into account in the design of thedevice, the mechanical stiffness of the bellows which may have aninfluence on the behavior of the device (impact on the power yield,direction of the forces, etc.). How this parameter is taken into accountwill be described in detail below.

However, the present invention is not limited to the use of bellows forforming the reservoir with variable volume. Thus, the person skilled inthe art may apply for producing the reservoir with a variable volume, apiston or a rolling membrane, which are considered as not having anymechanical stiffness. In this case, unlike the case of bellows, thestiffness will be considered as zero or negligible in the calculation ofthe pressure.

The movable portion of the reservoir has an effective pressure surfacearea which may be constant or variable according to the embodiment ofthe reservoir.

In the case of bellows, the effective pressure surface area isconsidered as constant and is given by the manufacturer. For a rollingmembrane, the effective pressure surface area varies according to theposition of the rolling membrane and is given by the manufacturer fordifferent travel values,

In the case of a piston sliding without any friction in a cylinder, theeffective pressure surface area is equal to the front surface area ofthe piston.

Actuator

The actuator may be selected from any electromechanical system allowingtransformation of electric energy into a mechanical movement with therequired power for allowing the displacement at a force and at arequired speed of the movable portion of the reservoir with variablevolume. For example mention may be made from among the actuators knownto the person skilled in the art, of piezo-electric actuators, ofelectromagnetic motors with or without brushes (in the case of abrushless motor, the latter may consist of 2 poles or of 4 poles) eithercoupled or not with a reducer, electro-active polymers or else shapememory alloys.

FIG. 2 illustrates an embodiment of the invention and represents asectional view of a portion of the inside of the casing 1.

The reservoir with variable volume 5 comprises a movable portion which,in this embodiment is bellows 9.

The bellows have a flange 6 coupled with a driving screw 17 via aspotted wheel 10 secured to the flange 6 and having tapping cooperationwith the threading of the screw 17.

The reservoir is delimited by a portion of the wall of the casing 1 andof the bellows 9.

The wall of the casing 1 moreover comprises a puncture port 4 which maybe perforated by a needle in order to add or withdraw fluid from thereservoir.

The reservoir 5 further comprises a connection 7 for tubing ensuring thefluidic connection with the occlusive sleeve (not shown).

The casing 1 further contains an actuator comprising a motor 13 coupledwith a reducer 8. A connector 12 allows the motor 13 to be powered whenthe control device transmits an order for operating the motor in onedirection or in the other depending on whether an increase or a decreasein the volume of the reservoir is required.

The reducer is coupled with a toothed wheel 18 which is itself coupledwith the driving screw 17, so as to transmit the torque and the rotationof the axis of the motor 13 to the driving screw 17. Rotation of thescrew 17 then drives the spotted wheel 10 into translation, which hasthe effect of displacing the flange 6 in translation in a directionparallel to the axis of the screw 17, the displacement direction of theflange 6 depending on the direction of rotation of the motor 13.

The inner space 11 of the casing surrounding the reservoir 5 is filledwith a gas.

The volume variation of the reservoir 5 therefore has the effect ofvarying the inner volume 11 and therefore the pressure of the gas insaid volume 11.

A gas pressure sensor (not shown) may optionally be laid out in thevolume 11 for measuring the pressure in this volume.

The toothed wheel 18 is housed in a block 15 via ball bearings 16 whichallow its rotation in the block 15. As the toothed wheel 18 is securedto the driving screw 17, the block 15 is driven into translation in thecasing by the screw 17. Pads 20 extend from the wall of the casing 1parallel to the axis of rotation of the screw 17 allowing guidance ofthe translation of the block 15.

A force sensor is attached on the wall of the casing facing the face ofthe block 15 opposite to the reservoir 5. The mark 19 refers to aconnector allowing transmission of the measurement data of the sensor tothe device for measuring and controlling the pressure.

In this embodiment, the force sensor 21 only measures compressiveforces.

In order to nevertheless allow measurement of the traction forces, thesystem comprises a pre-stress device 14 which exerts a determinedcompressive force on the force sensor. This pre-stress device thusgenerates an “offset” on the force sensor, which allows measurement ofboth the traction forces and the compressive forces.

Said pre-stress device may comprise one or several adjustment screwscooperating with the guiding pads 20 and, interposed between the head ofa respective adjustment screw and the block 15, a compressive spring, anextension spring and/or an elastomeric pad.

As this is seen, the integration of the force sensor to thepressurization system of the sleeve is particularly compact and istherefore not a penalty for the bulkiness of the implantable system.

FIG. 3 illustrates another embodiment of the invention and represents asectional view of a portion of the inside of the casing 1.

The elements bearing the same reference signs as in FIG. 2 fulfill thesame function and will therefore not be described again.

In this embodiment, the force sensor 22 may for example be based on ameasurement with strain gauge(s). The sensor 22 is attached on the block15 and on the wall of the casing facing said block, on the opposite sideto the reservoir. The force sensor 22 is able to measure bothcompressive and traction forces. The pre-stress device of the embodimentof FIG. 2 is not necessary in this case.

FIG. 4 illustrates an embodiment of the invention and represents asectional view of a portion of the inside of the casing 1.

In this embodiment, the movable portion of the reservoir 5 is notbellows but a rolling membrane 27. As in FIG. 2, the force sensor 21only measures compressive forces and is therefore associated with apre-stress device 14.

FIG. 5 illustrates another embodiment of the invention and represents asectional view of a portion of the inside of the casing 1.

The elements bearing the same reference signs as in FIG. 2 fulfill thesame function and will therefore not be described again.

In this embodiment, the force sensor 22 may for example be based on ameasurement with strain gauge(s). It may be integrated between thetapped spotted wheel 10 and the flange 6. The tapped spotted wheel 10and the force sensor 22 may also form a single and complete assemblyintegrating the strain gauge(s) and a tapped portion, thereby fulfillingthe force measurement and of drive by the driving screw 17. The forcesensor 22 is able to measure both compressive and traction forces. Thepre-stress device of the embodiment of FIG. 2 is not necessary in thiscase.

FIG. 10 illustrates another embodiment of the invention and illustratesa sectional view of a portion of the inside of the casing 1.

The elements bearing the same reference signs as on FIG. 2 fulfill thesame function and will therefore not be described again.

In this embodiment, the screw 17 is secured to the movable flange 6 ofthe bellows 9 and does not rotate. The linear movement of the flange 6of bellows 9 is performed by means of the rotation of the nut 10 whichlinearly drives the screw 17. The nut 10 is secured to the wheel 18which is driven by the reducer gear 8. The nut 10 is laid out so thatonly one rotation around the axis of the screw 17 is allowed. For this,a dual-effect bead abutment is laid out on the force sensor 22, by meansof beads 16 which allow the nut 10 to turn and support the experiencedforces along the axis of the screw 17. The forces exerted on the nut 10are identical with the exerted ones in the other configurations.

FIG. 11 illustrates the main forces experienced and measured by theforce sensor 22 with the purpose of inferring therefrom the pressure inthe fluidic circuit. For measuring force in the two directions along theaxis of the screw 17, the force sensor 22 is integrated into the beadabutment 16 so as to be able to measure forces in both directions. Thesupports 29 give the possibility of maintaining the force sensor 21. Inthis embodiment, the forces 23, 25 and 26 are measured by the forcesensor at the bead abutment 16 integrated into the driving nut 10. Theforce sensor may be in this case a sensor comprising strain gaugesplaced so as to measure forces in both directions along the axis of thescrew 17 secured to the flange 6 of the bellows 9.

The embodiment illustrated in FIGS. 10 and 11 has the advantage ofallowing a gain in space and gives the possibility of obtaining a largertravel of the bellows for the same dimensions of the implant, ascompared with other embodiments. The mechanical integration is moreoversimpler.

Determination of the Pressure in the Fluidic Circuit of the OcclusionSystem

The pressure in the fluidic circuit is determined indirectly. As thiswas indicated in the preamble, the integration of a pressure sensor onone of the walls of the reservoir of variable volume or on one of theportions of the fluidic circuit would be a restriction and would haveseveral drawbacks.

Instead of such a sensor, the present invention uses the movable portionof the reservoir with variable volume for indirectly measuring thepressure in the fluidic circuit of the occlusive system.

The implantable system therefore comprises a device for measuring thefluid pressure in the fluidic circuit, which comprises said force sensorand a processing unit (for example a microprocessor) coupled with saidsensor. The processing unit takes into account the force measurementsacquired by said sensor, as well as other mechanical, physical anddimensional parameters of the system, for determining the fluid pressurein the fluidic circuit.

In order to measure a relative pressure in the fluidic circuit, a sensor(for example a barometric sensor) allowing measurement of the currentatmospheric pressure may be laid out in an external device borne by thepatient in order to take into consideration the changes of atmosphericpressure related to the altitude and/or weather conditions.

Another embodiment may be based on the measurement of the currentatmospheric pressure directly from the fluidic circuit when one is sureunder determined conditions of having a pressure in the fluidic circuitequal to a known relative pressure (for example, zero relative pressurefor a particular position of the movable portion of the reservoir).

The measurement of the atmospheric pressure is then taken into accountin both embodiments described below for inferring therefrom a relativepressure from a measurement of absolute pressure as described below.

The description below is based on a force sensor only measuring thecompression (not traction). The same principle may be applied for forcesensors measuring compressions and tractions. In this case, one doeswithout the pre-stress system allowing generation of an “offset” on theforce for measuring both compressive and traction forces.

FIG. 6 illustrates the different forces measured by the force sensor,within the scope of the embodiment of FIG. 2:

-   -   the mark 23 refers to the force relatively to the pressure in        the fluidic circuit;    -   the mark 24 refers to the pre-stress force;    -   the mark 25 refers to the force related to the stiffness of the        bellows;    -   the mark 26 refers to the force related to the gas pressure in        the casing.

FIG. 7 illustrates the different forces measured by the force sensorplaced at the tapped spotted wheel 10 and at the movable wall 6, withinthe scope of the embodiment of FIG. 5:

-   -   the mark 23 refers to the force relative to the pressure in the        fluidic circuit;    -   the mark 25 refers to the force related to the stiffness of the        bellows;    -   the mark 26 refers to the force related to the gas pressure in        the casing.

In order to infer the pressure P1 in the fluidic circuit, the consideredparameters are the following:

S_(eff): the effective pressure surface area of the movable portion ofthe reservoir with a variable volume (as indicated above, this surfacearea may be fixed or variable depending on the configuration of thesystem);

F_(prest): the force generated by the pre-stress system;

K: the stiffness related to the reservoir with variable volume (case ofbellows for example), the latter may be neglected in certainconfigurations of the reservoir of variable volume (the case of a systemwith a rolling membrane or a piston);

i: the relative position of the movable portion of the reservoir with avariable volume relatively to a reference position,

F_(losses): the mechanical losses related to friction of the differentmechanical parts during transmission of the forces on the force sensor.

F_(sensor): the force measured by the force sensor(s).

P_(casing): the pressure of the gas contained in the implantablehermetic casing, said pressure may either be inferred from the positionof the movable portion relatively to its reference position and from theeffective pressure surface area of the movable portion, or be measuredby a gas pressure sensor placed in the casing (optional).

From these elements, several forces applied on the movable wall of thereservoir with a variable volume may be inferred therefrom:

F_(occl): the (positive or negative) force reduced on the movableportion of the reservoir of variable volume related to the pressure inthe fluidic circuit of the occlusion system;

F_(casing): the (positive or negative) force reduced on the movableportion of the reservoir of variable volume related to the pressure inthe implantable hermetic casing;

F_(wall): the force related to the position and to the stiffness of themovable portion of the reservoir of variable volume.

Subsequently it is considered that the gas pressure in the casing isinferred from the position of the movable portion relatively to itsreference position and from the effective pressure surface area of themovable portion.

The balance of the forces on the force sensor is expressed in thefollowing way:F _(sensor) =F _(occl) +F _(prest) −F _(wall) −F _(casing) −F _(losses)

with:

F_(occl) = P ⋅ S_(eff) F_(wall) = K ⋅ i$F_{casing} = {P_{init} \cdot ( {\frac{V_{init}}{V_{init} - {S_{eff} \cdot i}} - 1} ) \cdot S_{eff}}$

with P_(init) and V_(init) being constants corresponding to the initialpressure and the initial gas volume respectively in the casing when thelatter has been hermetically sealed.

P_(init) may for example be equal to atmospheric pressure when thecasing is hermetically sealed.

The force generated by the pre-stress device allows generation of an“offset” on the force sensor which allows measurement of positive andnegative forces.

The F_(casing) force is inferred from the position of the movable wallrelatively to its origin and from the effective pressure surface area ofthe movable wall. In this case it is considered that the casing isperfectly hermetic. It is also possible to assume a negligible loss ofgas of the casing outwards which may either be neglected or taken intoaccount in the calculation of the force F_(casing). Finally, the forceF_(casing) may also be directly measured by a pressure sensor andinferred by multiplying by the surface S_(eff).

The pressure P1 of the fluidic circuit of the occlusion system maytherefore be inferred therefrom:

${P\; 1} = \frac{F_{sensor} - F_{prest} + F_{wall} + F_{casing} + F_{losses}}{S_{eff}}$${P\; 1} = {\frac{F_{sensor} - F_{prest} + {K \cdot i} + F_{losses}}{S_{eff}} + {P_{init} \cdot ( {\frac{V_{init}}{V_{init} - {S_{eff} \cdot i}} - 1} )}}$

with F_(prest) and F_(losses) being known constants.

The force F_(prest) may be generated by pre-stressed springs. As thedisplacement of the block 15 is very small, it may considered that thetravel of the springs may be neglected relatively to their stiffness andthat the pre-stress force is constant.

F_(prest) is selected so as to be able to measure negative and positivepressures over the whole desired measurement range.

In the case when the force sensor is capable of measuring compressiveand traction forces, it is possible to remove the pre-stress system(case of the embodiments described in FIG. 3 and FIG. 5). In this case,the constant F_(prest) is not considered in the calculations of P1.

In order to infer the relative pressure P2 in the fluidic circuit, thecurrent atmospheric pressure exerted on the body of the patient shouldbe taken into account. The measurement of the pressure Patm may beachieved as described in the previous paragraphs.

In this case, P2 is calculated in the following way:P2=P1+(Pinit−Patm)

In a preferred embodiment, the casing is sealed so as to maximize theair volume in the casing (movable portion of the reservoir in an initialposition so as to have a minimum volume in the reservoir of variablevolume). This gives the possibility of having a pressure of the gas inthe casing always positive regardless of the position of the movablewall.

The paragraphs below show two examples of measurement of the pressurefrom the method described in the present invention.

The device described in both examples below has the followingcharacteristics:

-   -   S_(eff)=1×10⁻³ m²    -   K=5 N/mm    -   F_(prest)=20 N    -   V_(init)=10×10⁻⁵ m³    -   P_(init)=1,000 hPa    -   P_(atm)=900 hPa    -   F_(losses)=0 N

We have considered in these examples that the atmospheric pressureduring the sealing of the casing (Pinit) is different from theatmospheric pressure (Patm) exerted on the body of the patient duringthe measurement of the pressure in the fluidic circuit.

Example 1: measurement of the pressure in the fluidic circuit from adevice according to the embodiment described in FIG. 2, comprising aforce sensor only measuring compressive forces.

For i=0 (upper position of the bellows, corresponding to a minimumvolume of the reservoir), the processing unit performs the followingcalculation for measuring the pressure P1 in the fluidic circuit:

${P1} = \frac{F_{sensor} - {20}}{1 \times 10^{3}}$

For a relative zero pressure in the fluidic circuit for example, theforce sensor measures the compressive force of the pre-stress (20 N), aswell as the force related to the atmospheric pressure difference (900hPa) exerted on the body of the patient and therefore on the flexibleocclusive sleeve and the gas pressure in the casing (1,000 hPa) i.e. avalue P1 calculated by the processing unit:

Fsensor = 20  N + Seff × (Patm − Pinit)Fsensor = 20  N + 1.10⁻³ × (90000 − 100000) = 10  N${P\; 1} = {\frac{{10} - {20}}{1 \times 10^{- 3}} = {{- 10}\mspace{14mu}{kPa}}}$

The relative pressure P2 in the fluidic circuit may be inferredtherefrom:P2=P1+(Pinit−Patm)P2=−10000+(100000−90000)=0 Pa

For a relative pressure in the fluidic circuit of 5 kPa for example, theforce on the force sensor is the one generated by the pressure in thefluidic circuit F_(occl) (i.e. 5 N), that of the pre-stress (i.e. 20 N),and that related to the atmospheric pressure (−10 N) or a resultingforce of 15 N, or a value calculated by the processing unit:

${P1} = {\frac{{15} - {20}}{1 \times 10^{- 3}} = {{- 5}{kPa}}}$

The relative pressure P2 in the fluidic circuit may be inferredtherefrom:P2=P1+(Pinit−Patm)P2=−5000+(100000−90000)=5 kPa

For a relative pressure in the fluidic circuit of −5 kPa for example,the force on the force sensor is the one generated by the pressure inthe fluidic circuit F_(occl) (i.e. −5 N), that of the pre-stress (i.e.20 N), and that related to the atmospheric pressure (i.e. −10 N) i.e. aresulting force of 5 N, i.e. a value calculated by the processing unit:

${P1} = {\frac{5 - {20}}{1 \times 10^{- 3}} = {{- 1}5{kPa}}}$

The relative pressure P2 in the fluidic circuit may be inferredtherefrom:P2=P1+(Pinit−Patm)P2=−15000+(100000−90000)=−5 kPa

For i=4 mm for example (low position of the bellows, generating a gascompression in the casing and a return force related to the stiffness ofthe bellows), the processing unit performs the following calculation formeasuring the pressure in the fluidic circuit:

${{P1} = {\frac{{F{sensor}} - {5 \times 4} + 20}{1 \times 10^{- 3}} + {100000 \times ( {\frac{10 \cdot 10^{- 5}}{{10 \cdot 10^{- 5}} - {{1 \cdot 10^{- 3}} \times {4 \cdot 10^{- 3}}}} - 1} )}}}{{P1} = {\frac{F{sensor}}{1 \times 10^{- 3}} + {100000 \times ( {\frac{10 \cdot 10^{- 5}}{{10 \cdot 10^{- 5}} - {{1 \cdot 10^{- 3}} \times {4 \cdot 10^{- 3}}}} - 1} )}}}{{P1} = {\frac{F{sensor}}{1 \times 10^{- 3}} + {4166,67}}}$

For zero relative pressure in the fluidic circuit for example, theforces on the force sensor are F_(prest) (20 N), F_(wall) (−20 N),F_(casing) (−4.167 N) and the force related to the atmospheric pressure(i.e. −10 N) i.e. a resulting force of −14.167 N, i.e. a valuecalculated by the processing unit:

${P1} = {{\frac{{- 1}4,167}{1 \times 10^{- 3}} + {4166,67}} = {{- 10}{kPa}}}$

The relative pressure P2 in the fluidic circuit may be inferredtherefrom:P2=P1+(Pinit−Patm)P2=−10000+(100000−90000)=0 Pa

For a relative pressure in the fluidic circuit of 5 kPa for example, theforces on the force sensor are F_(occl) (5 N), F_(prest) (20 N),F_(wall) (−20 N), F_(casing) (−4.167 N) and the force related to theatmospheric pressure (i.e. −10 N) i.e. a resulting force of −9.167N i.e.a value calculated by the processing unit:

${P1} = {{\frac{{- 9},167}{1 \times 10^{- 3}} + {4166,67}} = {{- 5}{kPa}}}$

The relative pressure P2 in the fluidic circuit may be inferredtherefrom:P2=P1+(Pinit−Patm)P2=−5000+(100000−90000)=5 kPa

For a relative pressure in the fluidic circuit of −5 kPa for example,the forces on the force sensor are F_(occl) (−5 N), F_(prest) (20 N),F_(wall) (−20 N), F_(casing) (−4.167 N) and the force related to theatmospheric pressure (i.e. −10 N) i.e. a resulting force of −19.167 N,i.e. a value calculated by the processing unit:

${P1} = {{\frac{{- 1}9,167}{1 \times 10^{- 3}} + {4166,67}} = {{- 15}{kPa}}}$

The relative pressure P2 in the fluidic circuit may be inferredtherefrom:P2=P1+(Pinit−Patm)P2=−15000+(100000−90000)=−5 kPa

Example 2: measurement of the pressure in the fluidic circuit from adevice based on the embodiment described in FIG. 5, comprising a forcesensor capable of measuring compressive forces and traction forces.

For i=0, the processing unit performs the following calculation formeasuring the pressure in the fluidic circuit:

${P1} = \frac{Fsensor}{1 \times 10^{- 3}}$

For a zero relative pressure in the fluidic circuit for example, theforce sensor only measures a force related to the atmospheric pressuredifference (900 hPa) exerted on the body of the patient, and thereforeon the flexible occlusive sleeve, and the gas pressure in the casing(1,000 hPa) corresponding to a force of −10N, i.e. a value calculated bythe processing unit:

${P1} = {\frac{{- 1}0}{1 \times 10^{- 3}} = {{- 1}0{kPa}}}$

The relative pressure P2 in the fluidic circuit may be inferredtherefrom:P2=P1+(Pinit−Patm)P2=−10000+(100000−90000)=0 Pa

For a relative pressure in the fluidic circuit of 5 kPa for example, theonly force on the force sensor is the one generated by the pressure inthe fluidic circuit F_(occl) (i.e. 5 N), and the force related to theatmospheric pressure (i.e. −10 N) i.e. a value calculated by theprocessing unit:

${P1} = {\frac{- 5}{1 \times 10^{- 3}} = {{- 5}{kPa}}}$

The relative pressure P2 in the fluidic circuit may be inferredtherefrom:P2=P1+(Pinit−Patm)P2=−5000+(100000−90000)=5 kPa

For a relative pressure in the fluidic circuit of −5 kPa for example,the only force on the force sensor is the one generated by the pressurein the fluidic circuit F_(occl) (i.e. −5 N), and the force related tothe atmospheric pressure (i.e. −10 N) i.e. a value calculated by theprocessing unit:

${P1} = {\frac{{- 1}5}{1 \times 10^{- 3}} = {{- 1}5{kPa}}}$

The relative pressure P2 in the fluidic circuit may be inferredtherefrom:P2=P1+(Pinit−Patm)P2=−15000+(100000−90000)=−5 kPa

For i=4 mm, the processing unit performs the following calculation formeasuring the pressure in the fluidic circuit:

${{P1} = {\frac{{F{sensor}} - {5 \times 4}}{1 \times 10^{- 3}} + {100000 \times ( {\frac{10 \cdot 10^{- 5}}{{10 \cdot 10^{- 5}} - {{1 \cdot 10^{- 3}} \times {4 \cdot 10^{- 3}}}} - 1} )}}}{{P1} = {\frac{{F{sensor}} + 20}{1 \times 10^{- 3}} + {4166,67}}}$

For zero relative pressure in the fluidic circuit for example, theforces on the force sensor are F_(wall) (−20 N) and F_(casing) (−4.167N) and the force related to the atmospheric pressure (i.e. −10 N) i.e. aresulting force of −34.167 N, i.e. a value calculated by the processingunit:

${P1} = {{\frac{{{- 34},167} + 20}{1 \times 10^{- 3}} + {4166,67}} = {{- 10}{kPa}}}$

The relative pressure P2 in the fluidic circuit may be inferredtherefrom:P2=P1+(Pinit−Patm)P2=−10000+(100000−90000)=0 Pa

For a relative pressure in the fluidic circuit of 5 kPa for example, theforces on the force sensor are F_(occl) (5 N), F_(wall) (−20 N) andF_(casing) (−4.167 N), and the force related to the atmospheric pressure(i.e. −10 N) i.e. a resulting force of −29.167 N, i.e. a valuecalculated by the processing unit:

${P1} = {{\frac{{{- 29},167} + 20}{1 \times 10^{- 3}} + {4166,67}} = {{- 5}{kPa}}}$

The relative pressure P2 in the fluidic circuit may be inferredtherefrom:P2=P1+(Pinit−Patm)P2=−5000+(100000−90000)=5 kPa

For a relative pressure in the fluidic circuit of −5 kPa for example,the forces on the force sensor are F_(occl) (−5 N), F_(wall) (−20 N) andF_(casing) (−4.167 N), and the force related to the atmospheric pressure(i.e. −10 N) i.e. a resulting force of −39.167 N, i.e. a valuecalculated by the processing unit:

${P1} = {{\frac{{{- 3}9,167} + 20}{1 \times 10^{- 3}} + {4166,67}} = {{- 15}{kPa}}}$

The relative pressure P2 in the fluidic circuit may be inferredtherefrom:P2=P1+(Pinit−Patm)P2=−15000+(100000−90000)=−5 kPa

In both examples above, it is assumed that the device does not compriseany pressure sensor measuring the pressure of gas in the casing.

In a configuration where the device comprises a pressure sensormeasuring the gas pressure in the casing, it is sufficient to replacethe term

$F_{casing} = {{P_{init} \cdot ( {\frac{V_{init}}{V_{init} - {S_{eff} \cdot i}} - 1} ) \cdot S_{eff}}{with}P{sensor}}$

with Psensor being the measurement value of the gas pressure sensor.

It should be noted that the present invention may also be applied todevices including a reservoir with variable volume without anymechanical stiffness of the piston or rolling membrane type. In thiscase, the stiffness K in the calculation of the pressure P is consideredas zero or negligible.

Pressure Control of the Occlusive System

As the preferred goal of the system is to control the pressure, a closedloop regulation of the pressure first seems to be the wisest choice forthe pressurization of the occlusion system. However, the pressure in theocclusion system is not only dependent on the pressurization system.Outer effects related to the movements of the organs of the patient orto his/her breathing for example may generate pressures which will bemeasured by the pressure measurement system described earlier.

This may have the effect, during the pressure server control, ofinducing excessive stressing of the actuator and therefore a too largeelectric consumption. Indeed, the outer pressures may vary during achange in the pressure of the occlusion system, the server controlsystem will tend to try and compensate for these variations, which willgenerate excessive stressing of the actuator.

In order to find a remedy to this problem, one of the objects of thisinvention is to propose a simple method for controlling pressure of thepressurization system. Rather than subordinate the system as regardspressure, the actuator is controlled by position server control of themovable portion of the reservoir with variable volume. Knowing theeffective pressure surface area of the movable portion at each position,this therefore corresponds to a volume server control of the occlusionsystem.

Tests conducted in vitro and in vivo ([1]) have shown that therelationship between the pressure in the fluidic circuit and the volumeinjected into the occlusion system have a defined and repeatablerelationship over time. This is true under particular conditions of thepatient, i.e. when the latter is motionless and in a determined position(stretched out or standing for example).

The device for controlling the fluid pressure in the fluidic circuitnotably comprises a memory in which is recorded a relationship betweenthe pressure in the fluidic circuit and the volume injected from or tothe reservoir, a processing unit (optionally identical with theprocessing unit of the device for measuring the pressure in the fluidiccircuit) and a calibration unit, the operation of which is describedhereafter.

FIG. 8 is a graph illustrating the variation of the pressure in thefluidic circuit versus the volume injected into the fluidic circuit fromthe reservoir. It should be noted that the pressure relationshipdepending on the injected or removed volume may have hysteresis, i.e.the pressure curve during a rise in pressure may be different from thepressure curve during a drop in pressure. In order to be able to controlthe system as regards pressure, the pressurization system regularlyconducts pressure measurements for given injection volumes. Thiscalibration procedure is carried out under predetermined conditions. Forexample in the case of an artificial urinary sphincter, the calibrationmay be achieved a few minutes after urination and when the patient isstanding and substantially motionless. For this purpose, thepressurization system gradually increases the pressure for predeterminedinjection volumes and records the measured values in a table localizedin the memory of the implant. This calibration procedure may be carriedout at a defined time period, for example every week, or else upon anexamination by a physician, by means of a programmer in wirelesscommunication with the implant. In every case, the current atmosphericpressure should be able to be recovered for carrying out an accuratepressure measurement in the fluidic circuit regardless of the altitudeor of the weather conditions of the location where the patient is foundduring the calibration.

FIG. 9 is a graph illustrating the variation 28 of the pressure P2 inthe fluidic circuit versus time t for different fluid volumes injectedinto the occlusive sleeve during the calibration procedure.

The calibration may be carried out additionally when the patient is in astretched-out position and substantially motionless. This gives thepossibility of recording pressure values which will be different fromthose recorded when the patient is standing, because of the water columnbetween the implantable casing and the occlusive sleeve implanted atdifferent heights in the patient.

The calibration may take into account the hysteresis which may exist inthe fluidic circuit. In this case, the memory of the implant includes atable containing the values of the volume to be injected in order toattain a given pressure as well the values of the volume to be withdrawnin order to attain a given pressure.

During normal operation, when a command for pressurization at a givenpressure is sent to the pressurization system, the volume correspondingto the set pressure value is looked up in the table in memory and isused for pressurizing the occlusion system to the desired pressure.

As a safety step, the pressure may be measured during the pressurizationphase in order to ensure proper operation of the device and a match withthe expected pressure values.

In order to measure the movement of the patient and determine whetherhe/she is motionless, and for measuring his/her posture and determinewhether he/she is standing or stretched out, an accelerometer may beused.

In order to achieve the procedure for calibrating the volume versus thepressure in the occlusion system, a clock is used. For example it may beof the RTC type.

Safety System

In the case when the pressure in the fluidic circuit becomes very highand close to the limits defined in the technical recommendationsrelating to the pressure strength of the different elements of thefluidic circuit, the processing unit may automatically send an order fordecompressing the occlusive sleeve.

According to a particularly advantageous embodiment of the invention,the device for actuating the sleeve comprises a member for reducing themechanical stresses caused by too large pressure in the fluidic circuit,giving the possibility of protecting the actuation device from risks ofdeterioration.

The mechanical stresses experienced by the actuation device resultingfrom too large pressure in the fluidic circuit may become verysignificant, which may cause deterioration of one or more of theportions of the actuation device. The pressurization system, the tubing,the sleeve, the pressure sensor and/or the connectors may be concernedby this degradation.

In order to avoid deterioration of the actuation device, thestress-reducing member is designed for, when the mechanical stresses(pressure in the fluidic circuit) exceed a determined stress threshold,absorbing a portion of said stresses so as to reduce the stressesexperienced by the actuation device.

The stress-reducing member is dimensioned so as to reduce the stressesdown to a level at which they are too low for a risk of damaging theactuation device while being sufficiently high so as to not totallyrelease the compression exerted by the sleeve.

Depending on the contemplated method for reducing stresses and on thestructure of the actuation device, the person skilled in the art is ableto design a member fulfilling these conditions.

According to an embodiment, the stress-reducing member comprises anexpansion chamber laid out in the hydraulic circuit and beingmechanically triggered when the pressure in the fluidic circuit exceedsa defined threshold. This has the effect of transferring a portion ofthe fluid of the hydraulic circuit towards the expansion chamber inorder to reduce the pressure in the latter.

Alternatively, the stress-reducing member may comprise a piston coupledwith a spring system having a sufficiently high stiffness for remainingsubstantially fixed when the pressure in the hydraulic circuitcorresponds to the normal operating pressure of the device and movableunder the effect of a higher pressure.

The stress-reducing member may have different embodiments; for exampleand in a non-limiting way:

-   -   a valve coupled with a spring or a specific material in an        expansion chamber;    -   a component of the hydraulic circuit made in a flexible material        having the property of deforming from a certain pressure        threshold;    -   a deformable membrane beyond a certain pressure threshold or        depending on the applied pressure;    -   the reservoir with variable volume designed so as to be        deformable beyond a certain pressure threshold or depending on        the applied pressure;    -   the actuation mechanism designed so as to be deformable beyond a        certain pressure threshold or depending on the applied pressure.

REFERENCES

-   EP 1 584 303-   U.S. Pat. No. 8,585,580-   U.S. Pat. No. 4,581,018-   U.S. Pat. No. 4,222,377-   CA 1,248,303-   U.S. Pat. No. 4,408,597-   [1] Lamraoui, H; Bonvilain, A; Robain, G; Combrisson, H; Basrour, S;    Moreau-Gaudry, A; Cinquin, P; Mozer, P “Development of a Novel    Artificial Urinary Sphincter: A Versatile Automated Device”,    IEEE—ASME Transactions on Mechatronics, 15, 916-924, 2010.

The invention claimed is:
 1. An occlusion system implantable in a humanor an animal body, comprising: a fluidic circuit comprising: aninflatable occlusive sleeve containing a variable volume of a fluid,intended to surround at least one portion of a natural conduit to beoccluded, a reservoir with a variable volume filled with a fluid, saidreservoir comprising a fixed portion and a movable portion, the movableportion comprising a flange coupled to a nut and deformable bellowsextending or being compressed depending on a position of the flange, afluidic connection between the reservoir and the occlusive sleeve, anactuator mechanically coupled with the nut, the actuator beingconfigured to linearly displace the flange relative to the fixed portionfor adjusting a volume of the reservoir, the actuator and the reservoirboth being laid out in a sealed casing containing a gas, the systemfurther comprising: a sensor laid out in the casing, the sensor beingarranged on at least one of the flange and the nut, the sensor beingconfigured to measure at least one of a traction force and a compressiveforce in a direction of displacement of the movable portion of thereservoir.
 2. The system of claim 1, further comprising a processingunit configured to determine a fluid pressure in the fluidic circuitfrom a calculation taking into account at least the forces measured bythe sensor, an effective pressure surface area of the movable portion ofthe reservoir, and a force exerted on the movable portion of thereservoir with a variable volume related to a gas pressure in thecasing.
 3. The system according to claim 2, further comprising a devicefor controlling the fluid pressure in the fluidic circuit by the volumeof the reservoir, comprising: a memory in which is recorded arelationship between the pressure in the fluidic circuit and the volumeof said reservoir, a processing unit configured for: receiving a setfluid pressure value in the fluidic circuit, from the relationshiprecorded in the memory between the pressure in the reservoir and thevolume of the reservoir, determining the volume of the reservoir withwhich the set pressure value is attained, a calibration unit configuredfor: (a) with the body in a determined situation, controlling theactuator in order to displace the movable portion of the reservoir in aplurality of determined positions, each position defining a determinedvolume of the reservoir, (b) for each of set positions: determining thefluid pressure in the fluidic circuit with the processing unit, updatingthe memory by recording said measured fluid pressure in the fluidiccircuit for the respective volume of the reservoir.
 4. The system ofclaim 3, wherein the processing unit is further configured forcontrolling the actuator in order to displace the movable portion of thereservoir in a position defining the determined volume.
 5. The systemaccording to claim 2, wherein the processing unit is configured fortaking into account a stiffness of said bellows for determining thefluid pressure in the fluidic circuit.
 6. The system according to claim2, wherein the processing unit is configured for determining the fluidpressure during adjustment of the volume of the reservoir and forchecking a match between said determined value and an expected value. 7.The system according to claim 2, wherein the processing unit isconfigured for calculating a relative fluid pressure in the fluidiccircuit, said relative pressure being equal to a difference between thefluid pressure determined in the fluidic circuit, and an atmosphericpressure exerted on the body.
 8. The system according to claim 7,further comprising a device configured to be placed outside the body andcomprising a barometric sensor configured for measuring the atmosphericpressure exerted on the body, said device being configured forcommunicating said pressure measurement to the processing unit forcalculating said relative pressure of the fluid in the fluidic circuit.9. The system according to claim 8, wherein the processing unit isconfigured for determining the atmospheric pressure exerted on the body,from the pressure in the fluidic circuit and from a known relativepressure in a given actuation of the sleeve.
 10. The system according toclaim 1, wherein the actuator is selected from piezoelectric actuators,electromagnetic actuators, electro-active polymers and shape memoryalloys.
 11. The system according to claim 1, further comprising a gaspressure sensor laid out in the casing for measuring the gas pressure inthe casing, the processing unit being configured for taking into accountsaid measured gas pressure in the determination of the force.
 12. Thesystem according to claim 1, wherein a wall of the reservoir with avariable volume is formed by a wall of the casing, said wall comprisinga perforable puncture port.
 13. The system according to claim 1, furthercomprising a device for reducing stresses in the fluidic circuit basedon said stresses exceeding a determined threshold.
 14. The systemaccording to claim 1, further comprising an accelerometer, theprocessing unit being configured for, from measurement data of theaccelerometer, determining whether the body is in a determinedsituation.
 15. The system according to claim 1, comprising an artificialurinary sphincter.